Process for pumping gases using a chemically reactive aerosol

ABSTRACT

The specification describes a process and apparatus for pumping and removal of unwanted gases by effecting a chemical reaction between the gases and a highly reactive substance which is in the form of aerosol particles, to form a non-volatile, solid reaction product. In one embodiment of the invention, the reactive substance is initially provided in the form of a solid; the solid is heated to liquify it; and the liquid is forced through spray nozzles under high pressure to form the desired aerosol particles, which then react with the gas to be pumped.

This application is a continuation of application Ser. No. 960,681,filed Nov. 13, 1978, abandoned, from which divisional application Ser.No. 170,434 was filed July 21, 1980.

FIELD OF THE INVENTION

This invention relates to a pumping process and apparatus and moreparticularly to a pumping process which employs a chemical reaction withaerosol particles to remove unwanted gases.

BACKGROUND OF THE INVENTION

Although a variety of pumping processes have been used in the past toremove gases from a closed container, these processes are similar toeach other in that they all employ some physical means to move thegases. For example, a mechanical pump mechanically displaces the gas toremove it; a diffusion or ejector pump entrains gas molecules in a heavymolecular substance such as oil or steam; a cryogenic pump condenses thegas by means of application of a low temperature; a sorbent or getterpump binds the gas on the surface of sorbent molecules; and a blow-downsystem provides an evacuated chamber which the gas is allowed to fill.While these and other similar pumps perform their intended function(i.e., to raise, transfer or compress fluids), they have disadvantagesin some specialized applications, such as pumping a chemical laser,because of their high weight, large size, complex apparatus forimplementation, and significant operating costs. In addition, in certainapplications which require a short pump operating time (e.g., 5 to 500seconds), it is desirable to have a pump whose size scales with theoperating time. Most of the pumps mentioned above do not scale withoperating time and the pump size is determined solely by the requiredpumping rate. Furthermore, during the use of these pumps, the pumpedgases must be discharged, which could present a problem if these gasesare toxic or corrosive.

Such limitations make these pumps unsuitable for some airborne use andspace applications. In particular, there is a need for an efficient,compact, light-weight pump which can be used with a chemical laser toremove the flowing reaction product gases and to maintain a pressure of5 torr or less so that the lasing action can occur. These lasers areused in various applications where a high density of energy is requiredat a target surface, including such end-item uses an electroniccountermeasures devices, target designators, weapons systems and radarsystems.

There is one known process which differs from the pumps previouslymentioned in that it uses a chemical reaction to remove gases. This typeof pump is known as a solid-bed chemical pump and removes gases by agas-solid chemical reaction. A reactive solid, such as calcium (Ca), isformed into pellets of high surface area. These pellets are then placedin a chamber and the gas to be removed is introduced into the chamber. Achemical reaction occurs between the calcium and the gas, a solidreaction product is formed on the surface of the Ca pellets, and thusthe gas is removed. For example, if the gases to be removed are hydrogenfluoride (HF) and nitrogen (N₂), the bulk chemical reactions would be:

2Ca+2HF→CaF₂ +CaH₂

3Ca+N₂ →Ca₃ N₂

There are, however, several disadvantages in the solid-bed (calcium)chemical pump. The primary disadvantage is that the solid-bed Ca pump iscomplex and expensive both to fabricate and to operate. In addition,preparation of the Ca pellets used in this type of pump involves acostly, dangerous, and time-consuming process. Furthermore, once thepellets have been prepared, they are subject to violent explosions whencarelessly exposed to air. Further difficulties encountered in theoperation of a solid-bed Ca pump are that it requires a vacuum sealprior to use and it requires extensive maintenance to replace spent Capellets. In addition, during the use of such a pump, dangeroustemperature increases can occur for extended run times (e.g., greaterthan 5 seconds) because of the inability of the Ca pellets toefficiently dissipate the heat generated by the chemical reaction of thegases and Ca. This problem arises because the highly porous structure ofthe Ca pellets is not an efficient structure for the conduction of heat.However, this pellet structure is necessary in order to have a highsurface area of Ca available for chemical reaction. The more the surfacearea of the Ca is increased by increasing the porosity of the solid Ca,the greater the heat transport problem becomes. When the heat ofreaction is not dissipated, the Ca pellets themselves attain excessivetemperatures and some reaction products initially formed are decomposedby the heat (i.e., the chemical reaction is reversed), and the solid-bedCa pump does not function. This limitation makes the solid-bed Ca pumpof limited application for a chemical laser system that might requirepumping for 5 to 500 seconds of continuous operation.

SUMMARY OF THE INVENTION

The general purpose of this invention is to provide a new and improvedprocess and apparatus for pumping and removing exhaust or waste gasesand which possesses most, if not all, of the advantages and functions ofthe above prior art pumps and related processes, while overcoming theirabove significant disadvantages. The present invention overcomes thesedisadvantages of the prior art processes related to complexity, expense,safety, ease of implementation, and heat transfer. Moreover, the presentinvention provides a new and improved process for pumping gases over awide operating range and uses an apparatus of simple construction whichmay operate for extended periods of time as required by certain types ofchemical laser systems.

The above general purpose of this invention is accomplished by providinga new and improved process for pumping selected gates by converting theminto a non-volatile, solid product. More specifically, the presentinvention provides a new and improved pumping process in which achemical reaction occurs between the gases to be removed and a highlyreactive substance which is in the form of aerosol particles.

In order to further accomplish this purpose, we have discovered anddeveloped a novel pumping process in which the gaseous material to beremoved (or waste or exhaust gas) is brought into contact with aerosolparticles of a highly reactive substance. An aerosol is used herein tomean a suspension of fine solid or liquid particles in a gas, and indiscussed further by A. G. Bailey, in "The Generation and Measurement ofAerosols," Journal of Materials Science, Vol. 9, page 1344 (1974). Achemical reaction occurs between the aerosol particles and the gaseousmaterial to form a solid non-volatile reaction product, thus removingthe gaseous material. In a preferred embodiment, the highly reactivesubstance is provided in solid form, liquefied by heat, and then causedto flow through an aerosol-producing means.

In order to carry out our invention and its intended purpose as statedabove, we have also discovered and developed a new apparatus forimplementing the novel process of pumping gases by chemically reactingthem with aerosol particles of a chosen reactive substance.

Accordingly, it is an object of the present invention to provide a newand improved process for removing certain unwanted gaseous materials.

Another object is to provide a new and improved process for convertingcertain waste or exhaust gases into solid form, thus eliminatingpossibly hazardous exhaust products.

A further object is to provide a new and improved pumping process whichemploys a chemical reaction with aerosol particles to remove unwantedgases in a direct and highly controllable manner.

Another object is to provide a process of the type described which has awide operating range of pumping speeds and the capability of pumping ata high gas volume flow rate.

Another object is to provide a process of the type described which iscapable of operating over a wide pressure range.

Still another object is to provide a process of the type described whichis capable of maintaining high gas flow rates at low operating pressure.

Another object is to provide a process of the type described which canproduce a vacuum for a short duration and on a pulsed basis.

Yet another object is to provide a process of the type described inwhich the reactants are relatively safe and easy to handle and the firstreaction product is easily removed.

It is a further object of the present invention to provide a new andimproved apparatus for the implementation of the process describedabove.

A feature of the apparatus of the present invention is that it is simplein construction and requires no moving parts.

Another feature of the apparatus described is that is is comparativelylight in weight and of small size.

An additional feature of the apparatus described is that it is ranged,reliable and has reusable structural parts.

Another feature of the apparatus described is that it does not requirethe use of an auxiliary pump to produce an initial vacuum in order tofunction.

These and other objects and features of the invention will become morereadily apparent in the following description of the drawings andpreferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a flowchart for some of the major steps in one processembodiment of the present invention.

FIG. 2 is a schematic diagram of a simplified apparatus forimplementation of the process of the present invention.

FIG. 3 is a schematic diagram of an apparatus for implementation of theprocess of the present invention as it was reduced to practice.

FIG. 4 is a curve showing the reduction in chamber pressure versuselapsed time using the process and apparatus of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, step I indicates that a reactive substance isprovided in the form of a solid. This reactive substance may be lithium,sodium, potassium, calcium, a combination of these elements, or asimilar substance which has a high chemical affinity for the gases to beremoved and which generates precipitating non-volatile reaction productsas a result of reaction with these gases. The reactive substance may beprovided in the form of ingots, which are easy to handle. The solidreactive substance is placed in a chamber and, as indicated in step IIof FIG. 1, heat is applied at a temperature sufficient to cause thesolid to liquefy. In practice, heat is applied to the outside of thechamber containing the solid and the temperature of the solid ismonitored with a thermocouple. Optionally, the reactive substance may beinitially provided in liquid form. After the reactive substance has beenliquefied, an inert gas such as argon, neon, helium, xenon or kryptonpressurizes the reactive substance as indicated in step III of FIG. 1 toforce the liquid through nozzles designed to cause the liquid to breakup into small particles as the liquid flows through the nozzles. Thus, aspray or aerosol having particles of controlled size is generated. Next,as shown in step IV of FIG. 1, the aerosol particles of the reactivesubstance are brought into contact in a second chamber with the selectedgaseous materials to be removed. A vigorous chemical reaction occursbetween the gaseous material and the reactive aerosol, resulting in theformation of precipitating, non-volatile reaction products generating apartial vacuum in the second chamber, which provides the pumping andremoval of the gaseous material from its original container. Finally,after completion of the required pumping task, as step V of FIG. 1indicates, the solid reaction products can be removed by using anappropriate solvent to put at least some of the solids into solution andthen draining the resultant solution or slurry. Optionally, the solidreaction products may be removed by using removable walls within thesecond chamber and then removing the walls and the adhering reactionproducts after completion of the pumping task.

Turning now to FIG. 2, there is shown in simplified form an apparatusfor implementation of the process described in FIG. 1. A first chamber10, or antechamber, which receives the reactive substance in solid form,is provided with the openings 11 and 13. The opening 11 in the topsurface 9 of the chamber 10 receives a valve 12 which controls theinflux of the inert gas 14 through pipe 21 into the chamber 10. Theopening 13 in the bottom surface 8 of the chamber 10 is connected to anaerosol-producing means 16 which is also connected to a second chamber18. The aerosol-producing means 16 may contain a valve which controlsthe flow rate of the reactants into the second chamber 18. This valvemay be omitted, in which case the reactant flow rate is controlled bythe pressure of the inert gas 14 that is applied as discussed below. Thechamber 10 is also provided with the heating elements 22 on the outsidesurface of a portion of its vertical walls 6 and 7 and on the bottomsurface 8. When heat is applied to the walls 6, 7, and 8 of the chamber10, it is conducted to the solid reactive substance (not shown) and aliquid 24 is formed in the chamber 10. The second chamber 18, in whichthe reactive aerosol reacts with the gaseous material to be removed, isprovided with the openings 15, 17 and 19. The opening 15 in the topsurface 25 of the chamber 18 receives the aerosol-producing means 16which is also connected to the chamber 10, as discussed above. Theopening 17 in one vertical wall 26 of the chamber 18 passes the influxof the gaseous material 28 to be removed, into the chamber 18. Theopening 19 in the bottom surface 27 of the chamber 18 receives a drain30 and a plug 32 which are used to remove the solid reaction products 34after they have been put into solution. The opening 19 and the drain 30and plug 32 are not needed if the optional removable wall configurationis used, as discussed for FIG. 1. The chamber 18 is also provided withthe cooling elements 36 on the outside surface of the vertical walls 29and 31 and the bottom surface 27.

The apparatus of FIG. 2 is operated in accordance with the flowchart ofFIG. 1. First, a reactive substance in solid form is placed in thechamber 10 of FIG. 2. The heating elements 22 adjacent the first chamber10 are activated so that heat is applied to the reactive solidsufficient to cause it to form the liquid 24 of FIG. 2. Then, the inertgas 14 is applied under controlled pressure through the valve 12 intothe first chamber 10 to force the liquid 24 through theaerosol-producing means 16 to form the aerosol particles 20 in thesecond chamber 18. At the same time, the gaseous material 28 to beremoved is introduced through the opening 17 into the second chamber 18.A chemical reaction occurs between the aerosol particles 20 and thegaseous material introduced into the second chamber 18, and solidreaction products 34 form and settle on the interior walls and thebottom of the second chamber 18. While the chemical reaction is takingplace, the cooling elements 36 are activated to remove heat from thesecond chamber 18. After the reaction has been completed, the firstchamber 10 is separated from the second chamber 18. One method ofcleaning the second chamber 18 is to add water slowly to the chamber 18to react with the solid reaction products 34 to form a solution or aslurry, which is drained off through the drain 30 by removing the plug32. Similarly, the first chamber 10 may be cleaned by the slow additionof water.

Directing attention now to FIG. 3, there is shown a schematic diagram ofan apparatus as it was actually reduced to practice. A first chamber 40,or antechamber, which receives the reactive substance such as lithium insolid form, is constructed of stainless steel and is typically 6 incheswide and 9.5 inches high. The chamber 40 is provided with a top portion80 which is joined to the remainder of the chamber 40 by a number ofhardened steel bolts such as the bolts 82 and 84. A hollow O-ring madeof metal, such as a nickel alloy, (not shown) provides a seal betweenthe top portion 80 and the top open surface of the chamber 40. The topportion 80 of the chamber 40 is provided with the openings 41, 43, 45and 47. The first opening 41 in the top portion 80 receives a valve 42which controls the influx of argon, for example, under high pressure(typically 850 pounds per square inch) into the chamber 40. Bycontrolling the pressure of the argon and thus the flow rate of thereactant through the nozzle 52, the pumping speed can be controlled. Thesecond opening 43 in the top portion 80 receives a valve 44 whichprovides for relief of pressure in the chamber 40. If it is desired toterminate the flow of Li and thus the pumping process before the wholeingot of Li has been consumed, the valve 44 can be opened and thepressure in the chamber 40 relieved. Without the application of therequired gas pressure, Li flow stops and the pumping process ceases. Thethird opening 45 in the top portion 80 receives a thermocouple 46 whichis used to monitor the temperature of the contents of the chamber 40.The fourth opening 47 in the top portion 80 receives a pressureindicator 86 which is used to monitor the pressure in the chamber 40.

In addition, the chamber 40 is provided with an opening 49 in the bottomsurface 88 which receives a nozzle holder 48. A stainless steel meshfilter 50 is placed across the opening 49 in the bottom surface 88 ofthe chamber 40 where this opening abuts the top opening 51 in the nozzleholder 48. The filter 50 removes any solid impurities which may bepresent in the liquid and prevents them from passing into theaerosol-producing means where they might clog the openings. Theaerosol-producing means comprises the nozzle holder 48 which contains aplurality of stainless steel nozzles 52 which have openings ofpredetermined size for controlling the aerosol particle size. Thesenozzles 52 project into a second chamber 54 to be described below. Atthe bottom surface 88 where the nozzle holder 48 abuts the lower surfaceof the chamber 40, a hollow metal O-ring (not shown) is inserted toprovide efficient sealing. The chamber 40 is also provided with theheating elements 56 on the outside surface of the vertical walls 55 and57 and with heating elements (not illustrated) which are inserted in theopenings 69 near the bottom surface 88 of the chamber 40. When theheating elements 56 and those inserted in the openings 69 are activated,the walls 55, 57, and 88 of the chamber 40 are heated and this heat isconducted to the contents of the chamber 40, which is the reactivesubstance in solid form. When a sufficiently high temperature isreached, the solid turns to liquid and forms a pool in the bottom of thechamber 40. (Although lithium liquefies at 180° C., in practice thechamber 40 is maintained at an internal temperature of 450° C. topromote the pumping reaction.)

A second chamber 54, in which the reactive aerosol reacts with thegaseous material to be removed, is constructed of stainless steel, has acurved bottom, and is typically 16 inches wide and 19 inches high. Thevolume of the chamber 54 must be large enough to allow the aerosolparticles to remain suspended for a period of time sufficient to reactwith the incoming gaseous material. The bottom surface 59 of the chamber54 as shown in FIG. 3 is curved in order to provide additionalstructural stability, but this curved-bottom structure is optional. Thechamber 54 has an opening 53 in its top surface 61 which receives thenozzle holder 48 and thus connects with the chamber 40. An O-ring (notshown) made of Viton (a rubber substance manufactured by Parker Seals,Inglewood, California) is used to provide efficient sealing at thesurfaces 70 and 72 where the chamber 40 and the chamber 54 are joinedtogether by a number of hardened steel bolts such as bolts 74 and 76.Also, in the top surface 61 of the chamber 54 there is an opening 77that receives a pressure indicator 78, which is used to monitor thepressure in the chamber 54.

In one vertical wall 63 of the chamber 54, there is an opening 58typically 8 inches in diameter, with a flange 60 which provides accessinto the chamber 54 for the gaseous material 62 to be removed from itsoriginal container (not shown). The value for controlling the influx ofthe gaseous material 62 is located external to the apparatus of FIG. 3,at the source of or container holding the gaseous material. Parallel tothe opening 58 and within the chamber 54 is a gas flow deflector 64which provides an even flow of the gaseous material 62 in the chamber 54by preventing a straight-through flow of gas which would force thereactive aerosol particles against the walls of the chamber 54 andinterfere with the ability of the particles to react. The gas flowdeflector 64 is held in place by the screws 90 and 92. At the bottomsurface 59 of the chamber 54, there is an opening 65 which receives adrain tube 66 with a plug or cap 68. The tube 66 is used upon completionof pumping, to remove the solid reaction products after they have beenput into solution. The opening 65 in the chamber 54 and the drain tube66 may optionally be placed on a vertical wall of the chamber 54 nearthe bottom surface of the chamber. Finally, the chamber 54 is providedwith the cooling elements 94, for example, cooling pipes, on the outsidesurface of the vertical walls 63 and 67 and the bottom surface 59. Whenthe cooling elements 94 are activated, the walls 63, 67, and 59 of thechamber 54 are cooled and, in turn, the contents of the chamber 54 arecooled. Cooling is required in order to dissipate the heat produced bythe chemical reaction which occurs in the chamber 54. Example 1 providesa description of the operation of the apparatus of FIG. 3.

Turning next to FIG. 4, the data obtained upon actual reduction topractice is displayed on a semi-log plot to indicate the decrease inchamber pressure which occurred as time elapsed, using the presentinvention. The apparatus of FIG. 3 was used to pump nitrogen gas, usinga 75 liter volume initially charged with nitrogen at 350 torr at roomtemperature. "Pressure" in FIG. 4 refers to the pressure within thechamber 54 of FIG. 3. "Elapsed Time" in FIG. 4 refers to the duration oftime for which pumping was performed. Effective pumping action over therange of 350 torr to 10 torr is indicated in FIG. 4, in which the slopeof the curve is proportional to the moles per second per torr of gasespumped. Data have also been obtained to demonstrate the effectivepumping of nitrogen at pressures ranging from 650 torr to less than 5torr.

EXAMPLE 1

Using the apparatus described in FIG. 3, the present invention hasactually been reduced to practice to pump nitrogen (N₂)gas. Theapparatus of FIG. 3 was placed in a holding device which supported theapparatus by the protruding surface where the chambers 40 and 54 arejoined (below the bolts such as bolts 74 and 76). An ingot of filtered,battery grade lithium (Li), 99.8% pure, (obtained from Lithium Companyof American in Bessemer City, N.C.), was loaded into the chamber 40 ofFIG. 3. The top portion 80 of the chamber 40 was removed by removing theconnecting bolts as exemplified by the bolts 82 and 84 and the metalO-ring at the interface between the top portion 80 and the top opensurface of the chamber 40. The Li was inserted into the chamber 40 andthe metal O-ring, the top portion 80, and the connecting bolts similarto the bolts 82 and 84 were replaced. The cooling elements 94 wereactivated by applying a 5 gallon per minute flow of water. Heatingelements which consisted of cartridge heaters were inserted in theopenings 69 near the bottom surface of the chamber 40 and were activatedby the application of a controlled voltage. The heating elements 56,which consisted of a band heater strapped to the chamber 40, were alsoactivated by application of a controlled voltage, and a temperature of450° C. was maintained in the chamber 40. After the chamber 40 hadreached a stable temperature of 450° C., at which temperature the Lisolid had liquefied, argon gas at a pressure of 850 pounds per squareinch was applied through the valve 42 into the chamber 40. Thepressurized argon forced the liquefied Li through the nozzles 52, toform a spray of aerosol particles which were introduced into the chamber54. The nozzles used were obtained from Spraying Systems Company,Wheaton, Ill., and had an opening size at the exit of 0.016 inch. The Liflowrate per nozzle was 1.6 grams of Li per second and seven nozzleswere used. At the same time as (or after) the aerosol particles wereintroduced into the chamber 54, the gaseous material to be removed,i.e., nitrogen, was introduced into the chamber 54 through the flange60. The following chemical reaction is assumed to generate the observedpumping action:

6Li+N₂ →2Li₃ N.

The lithium nitride (Li₃ N), indicated by its observed red color,precipitated out and settled to the bottom of the chamber 54. Gaspumping speeds of up to 0.2 moles/second of N₂ (5.6 grams/second of N₂)at 250 torr have been measured. Lithium efficiencies have been measuredto be in excess of 0.5 grams of N₂ per second/gram of Li per second.This measured efficiency exceeds 75 percent of the theoreticallypossible value of 0.67 grams of N₂ per second/gram of Li per second,based upon the stoichiometry of the reaction. Effective pumping actionhas been accomplished over the pressure range from 650 torr to 5 torr ofnitrogen.

To clean the apparatus after pumping was completed, the chamber 40 wasseparated from the chamber 54 by removing the connecting bolts such asthe bolts 74 and 76. Then water was carefully and slowly added to thechamber 54. The following chemical reaction occurred:

Li₃ N+3H₂ O→NH₃ +3LiOH

The NH₃ dissipated as a gas and the LiOH dissolved in the excess waterto form a solution which was removed from the chamber 54 by removing theplug 68 from the drain tube 66 and allowing the solution to drain into asuitable waste container. To clean the chamber 40, the top portion 80was removed by removing the connecting bolts such as the bolts 82 and84, and water was carefully and slowly added to the chamber 40. Anyremaining Li reacted with the water as follows:

2Li+2H₂ O→2LiOH+H₂

The LiOH dissolved in the water and was poured out of the chamber 40.The H₂ escaped as a gas.

EXAMPLE 2

The present invention was also reduced to practice to provide exhaustgas pumping for a simulated hydrogen fluoride (HF) chemical laserexhaust, in a manner similar to that specified above for N₂.

In an HF laser, a hydrogen fluoride (HF) molecule is produced in anexcited state (HF*) which produces the lasing action. The associatedchemical reactions are as follows:

(1) D₂ +2F₂ →2DF+2F

(2) F+H₂ →HF*+1/2H₂

(3) HF*→HF+h

Thus, the waste gases from an HF laser system are: HF, DF, H₂ and N₂,the latter being used to cool the laser gases.

In practicing the present invention, using Li as the reactive substanceand HF laser exhaust gases as the exhaust gases, the following chemicalreactions occurred in the chamber 54 of FIG. 3:

HF+2Li→LiH+LiF

H₂ +2Li→2LiH

N₂ +6Li→2Li₃ N

Using the apparatus shown in FIG. 3, except that only one nozzle wasused, gas pumping speeds of 18 millimoles/second of HF laser exhaustgases (0.4 g/second of gases) were measured. Only H₂ and HF were used inthis example and the deuterium analogs were omitted since their chemicalproperties are the same.

When pumping had been completed, the solid reaction products werereacted with water. The following reactions occurred:

LiH+H₂ O→LiOH+H₂

Li₃ N+3H₂ O→3LiOH+NH₃

The LiOH dissolved in the water to form a solution; the LiF is insolublein water but formed a slurry in the solution of LiOH; and the slurry wasdrained off through the tube 66 of FIG. 3. The NH₃ and H₂ escaped fromthe open system as gases.

The present invention has the potential to overcome many of thedisadvantages of the prior art solid bed chemical pumping processpreviously discussed. First, the present invention is more simple andless expensive than the prior art solid bed Ca pump. The presentinvention can be easily implemented using the claimed apparatus whichhas no moving parts, consists of easily manufactured, rugged components,has reusable structural parts, and requires no permanent vacuum. Inaddition, there are no extensive maintenance requirements inimplementing the present invention. The present invention also overcomesprior art problems relating to safety and ease of implementation. In thepreferred embodiment discussed above, the present invention uses solidlithium in the form of ingots which may be obtained from a commercialsupplier. In this form, the lithium presents reduced safety hazards,compared to the prior art Ca pellets and may be handled in air. Also, inpracticing the present invention, the problem in conventional pumps ofremoving hazardous or toxic exhaust products is minimized because asolid reaction product is formed. The solid reaction product whichsettles on the walls and the bottom of the reaction chamber can beremoved by controlled reaction of water with the solids to form solubleproducts, which can then be drained off. With similar ease, when thelithium reactant is used up, merely cleaning the reactant reservoir andinserting a new lithium ingot makes the pump ready for use again.

In addition, a major disadvantage of the prior art process, asdiscussed, is the internal heat transport problem which arises from theinability of the calcium pellets to efficiently dissipate the heat ofchemical reaction. By contrast, using the present invention, heattransport is accomplished more effectively than the solid bed Ca pump sothat the problem of dangerous temperature increases is minimized. Heatis transported to the walls of the reaction chamber of the presentinvention by means of radiation, mass deposition of the aerosol onto thewalls, and convection. At elevated temperatures, radiation becomes thedominant heat transfer process. Both the rate of reaction and heattransfer by radiation are proportional to the surface area of theparticles. An increased reaction rate is, thus, accompanied by increasedheat dissipation, so that a steady state can be achieved and temperatureincreases are moderated. In order to achieve increased pumping speeds inpracticing the present invention, the dispersion of the aerosol may beincreased to increase the particle surface area without generating anexcessive temperature increase.

In addition to overcoming disadvantages of the prior art processes, thepresent invention has further advantages to offer not easily availablein the prior art. One important feature of the present invention is thatit offers a wide range of operating pressure. At fixed operatingpressure and temperature, the instantaneous pumping speed per unit massof injected aerosol material is proportional to the product of totalspecific aerosol area, A_(s), and the surface chemical rate constant,K_(s). The total specific aerosol area can be changed by changing theaerosol diameter in accordance with the following equation:

    A.sub.s =6/ρd.sub.o cm.sup.2 /gr

where

A_(s) =specific aerosol area

ρ=aerosol material bulk density (gr/cm³)

d_(o) =aerosol diameter (cm)

The diameter of the aerosol is influenced by the spray nozzle design andby adjusting the pressure of the inert gas which forces the reactiveliquid through the nozzle. Thus, by changing the diameter of the aerosolmaterial in the present invention, it is possible to effectively pumpgases over a wide range of flow rates. By appropriately scaling the rateof Li flow and the dimensions of the reaction chamber, the presentinvention can accommodate a wide range of gas flow rates. It isestimated that flow rates of at least 10 moles/second can be pumped. Inaddition, if the reactant is actively cooled, the aerosol pump operatingtime is limited only by the amount of reactant that is stored. Hence,the operating time may vary from short pulses to continuous operation.It has further been demonstrated that the present invention can performover a pressure range of approximately 0.01 to 1 atmosphere foroperating times of up to 300 seconds.

Furthermore, the present invention has a distinct potential advantageover the majority of prior art processes by virtue of the fact that theapparatus used for its implementation is much lighter in weight andsmaller than many conventional pumping apparatus. If a pump is beingused in conjunction with a chemical laser, a conventional pump could beas much as 75 percent of the total weight of the system. On the otherhand, the claimed apparatus of the present invention may be only 10 to30 percent by weight of the total system. The low weight and small sizeof the apparatus of the present invention make it particularly suitedfor airborne use and space applications. Also, the present inventionoffers a significant advantage in applications which have a low dutycycle because the size of the pump scales with the required operatingtime.

The present invention is also particularly suited for application tochemical laser systems, where there is the requirement for pumpingexhaust gases for short periods of time (i.e., pulsed), to produce a lowpressure at a high gas flow rate. In addition, there is the advantage inusing the present invention that the toxic exhaust gases HF and DF areeliminated.

Thus, the present invention not only overcomes the disadvantages ofprior art processes associated with complexity, expense, safety, ease ofimplementation and heat transfer, but also offers the further advantagesof a wide range of pumping speeds and operating pressures, light weightand small size.

While the invention has been particularly described with respect to thepreferred embodiments thereof, it will be recognized by those skilled inthe art that certain modifications in form and detail may be madewithout departing from the spirit and scope of the invention. Inparticular, the scope of the invention is intended to include thereaction of exhaust gases with reactive aerosol particles which may beformed by means other than those described herein. The reactivesubstance may be provided in liquid as well as solid form. Furthermore,in the apparatus described, the particular dimensions indicated may bevaried and the position of the openings, such as those for the influx ofexhaust gas and for the influx of reactive aerosol, may be varied on thesurfaces shown and may be on different surfaces than those shown.

What is claimed is:
 1. A process for pumping a selected gaseous material to remove it from a container which comprises:(a) providing a chosen highly reactive substance in solid form; (b) heating said solid highly reactive substance at a predetermined elevated temperature sufficient to change said solid to a liquid; (c) causing said liquid to flow through a means for dispersing said liquid into aerosol particles; and (d) mixing said aerosol particles with said gaseous material in a reaction chamber to cause a chemical reaction therebetween of the type sufficient to form a solid, nonvolatile reaction product and to thereby generate a partial vacuum in said chamber and provide the pumping of said gaseous material from said container.
 2. The process as set forth in claim 1 wherein said liquid is caused to flow through said dispersing means by applying to said liquid a chosen inert gas under predetermined pressure.
 3. The process as set forth in claim 2 wherein said inert gas is chosen from the group consisting of argon, neon, helium, xenon, and krypton.
 4. The process as set forth in claim 1 wherein the selected gaseous material is removed to thereby produce a pressure of 1 torr or more in the original container of said gaseous material.
 5. The process defined in claim 1 wherein said highly reactive substance is selected from the group consisting of lithium, sodium, potassium, calcium, mixtures thereof, and a substance which has a high chemical affinity for said gaseous material and forms solid, non-volatile products by reaction with said gaseous material.
 6. The process defined in claim 1 wherein said gaseous material is selected from the group consisting of nitrogen; oxygen; a mixture comprising nitrogen, hydrogen, deuterium, and hydrogen flouride; and a gas which is capable of reacting with said reactive substance to form a solid, non-volatile product.
 7. A process for pumping certain exhaust gases from a container therefor by converting said gases into solids suitable for solution into and transport by a selected liquid transporting medium, which comprises:(a) providing a chosen highly reactive substance in liquid form, said reactive substance being selected from the group consisting of lithium, sodium, potassium, calcium, mixtures thereof, and a substance which has a high chemical affinity for said exhaust gases and forms solid, nonvolatile products by reaction with said exhaust gases; (b) causing said liquid to flow through a means for dispersing said liquid into aerosol particles by applying to said liquid a chosen inert gas under predetermined pressure; and (c) mixing said exhaust gases selected from the group consisting of nitrogen; oxygen; a mixture comprising nitrogen, hydrogen, deuterium, and hydrogen fluoride; and a gas which is capable of reacting with said reactive substance to form a solid, nonvolatile product, with said particles in a reaction chamber to cause a chemical reaction between said particles and said gases, of the type sufficient to form a solid reaction product which deposits in a chosen location and to thereby generate a partial vacuum in said chamber.
 8. The process as set forth in claim 7 wherein said inert gas is selected from the group consisting of argon, neon, helium, xenon, and krypton. 